1. Field of the Invention
The present invention relates to a position detection apparatus which detects an edge position of a sheet passing through a sheet conveying path and an image forming apparatus including the position detection apparatus.
2. Description of the Related Art
Conventionally, there is an image forming apparatus, such as a copying machine and a printer, having a duplex printing function which forms an image on a first side of a sheet (hereinafter referred to as “simplex printing”) and thereafter reverses the sheet and forms an image on a second side opposite to the first side (hereinafter referred to as “duplex printing”).
When the duplex printing is performed in such an image forming apparatus, a sheet conveying path to a position at which the duplex printing is performed (for example, a path in which a sheet where the simplex printing has been completed is reversed and conveyed to an image forming unit) is longer than a path used for the simplex printing. Therefore, due to influence of a small alignment error of a conveying roller, deformation of a guide plate, and the like, there is a risk that the sheet gradually moves in a sheet width direction perpendicular to a sheet conveying direction and an image formed on the sheet is shifted in the sheet width direction.
To solve the above problem, a position detection apparatus is proposed which detects an amount of positional shift of an edge position in the sheet width direction of the sheet in the sheet conveying path by a line sensor and determines a print start position of the duplex printing based on the detection result (see Japanese Patent Laid-Open No. 2002-292960). In the position detection apparatus described in Japanese Patent Laid-Open No. 2002-292960, to detect edge position of sheets being conveyed from a minimum size to a maximum size, a line sensor is arranged in a line, light is irradiated from one side of the sheet, and the edge position in the sheet width direction is detected from a light blocking state.
However, the position detection apparatus described in Japanese Patent Laid-Open No. 2002-292960 detects the edge position in the sheet width direction of sheets of all sizes that can be conveyed, so that a line sensor that can detect the edge position in the sheet width direction of sheets of all sizes is required. Therefore, the cost of the sensor itself increases, causing a problem that the cost of the entire apparatus increases.
To solve the above problem, a position detection apparatus is proposed which detects the edge position in the sheet width direction perpendicular to the sheet conveying direction by using a moving holder having a pair of sensors that includes a light emitting portion and a light receiving portion (for example, a photo-interrupter) (see Japanese Patent Laid-Open No. 05-132193). The position detection apparatus described in Japanese Patent Laid-Open No. 05-132193 moves the moving holder in the sheet width direction so that the edge of the sheet traverses between the light emitting portion and the light receiving portion which are disposed to face each other, and detects the edge position in the sheet width direction by the distance from a reference position to a light path blocking position.
However, since the position detection apparatus described in Japanese Patent Laid-Open No. 05-132193 detects the edge position in the sheet width direction by one pair of sensors, it is necessary to secure a long moving distance of the moving holder to detect the edge position in the sheet width direction of sheets of a plurality of sizes. To secure the moving distance of the moving holder, for example, it is necessary to enlarge the moving mechanism and, therefore, there is a risk that the apparatus itself is enlarged.
To solve the above problem, for example, a plurality of pairs of sensors is arranged on the moving holder in the sheet width direction so that the pairs of sensors respectively correspond to the edge positions of sheets of a plurality of sizes. Accordingly, it is possible to shorten the moving distance of the moving holder and prevent the moving mechanism from being enlarged.
However, when a plurality of pairs of sensors is arranged in the sheet width direction, for example, light emitted from a light emitting portion may be received by a light receiving portion adjacent to a light receiving portion facing the light emitting portion and, therefore, there is a risk of detection error.
To solve the above problem, for example, a plurality of pairs of sensors is arranged at positions corresponding to the sizes of sheets to be conveyed. Only the pair of sensors arranged at a position corresponding to the size of a sheet to be conveyed is moved so that it is possible to prevent the detection error of the adjacent pair of sensors. However, if a plurality of pairs of sensors is moved, electric circuits, the number of which corresponds to the number of the pairs of sensors, are required. Accordingly, the cost increases and space for storing wiring is required. Also, there is a risk that the apparatus itself is enlarged.
Therefore, the present invention provides a position detection apparatus which can detect an edge position of a sheet in the sheet width direction with a high degree of accuracy using an inexpensive and simple configuration and an image forming apparatus including the position detection apparatus.